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A defense air force plane, diving with constant speed at an angle of \(52.0^{\circ}\) with the vertical, drops a shell at an altitude of \(720 \mathrm{~m}\). The shell reaches the ground \(6.00 \mathrm{~s}\) after its release. (a) What is the speed of the plane? (b) How far does the shell travel horizontally during its flight? What are the (c) horizontal and (d) vertical components of its velocity just before reaching the ground? Assume an \(x\) axis in the direction of the horizontal motion and an upward \(y\) axis.

Short Answer

Expert verified
(a) \(6.44\,\text{m/s}\), (b) \(30.48\,\text{m}\), (c) \(5.08\,\text{m/s}\), (d) \(53.86\,\text{m/s}\).

Step by step solution

01

Analyze Motion in Vertical Direction

The shell is dropped from a height of \(720\, \text{m}\) and it takes \(6.00\, \text{s}\) to reach the ground. Use the equation of motion in vertical direction \(y = v_{y0}t + \frac{1}{2}gt^2\). Since the initial vertical velocity is neither specified nor needed for calculating the initial horizontal velocity, we first find the vertical component of velocity \(v_{y0}\). The acceleration \(g = 9.81\, \text{m/s}^2\). Setting \(y = -720\, \text{m}\) (since the shell falls) : \[-720 = v_{y0} \times 6 + \frac{1}{2} \times 9.81 \times 6^2\] Solving for \(v_{y0}\) gives: \[v_{y0} = \frac{-720 - \frac{1}{2} (9.81)(6^2)}{6} = -5.0\, \text{m/s}\] (downward)
02

Calculate Magnitude of Velocity

Given the initial velocity angle \(52.0^{\circ}\) with the vertical, we can express the total initial velocity of the shell. Use trigonometric relations: \[v_{y0} = v_0 \cos(52.0^{\circ})\] Substitute \(v_{y0} = -5.0\, \text{m/s}\) to find the magnitude of velocity \(v_0\): \[-5.0 = v_0 \cos(52.0^{\circ})\] \[v_0 = \frac{-5.0}{\cos(52.0^{\circ})} = -6.44\, \text{m/s}\] (approximate)
03

Calculate Horizontal Component of Initial Velocity

The horizontal component \(v_{x0}\) of the initial velocity is expressed using: \[v_{x0} = v_0 \sin(52.0^{\circ})\] Substitute \(v_0 = -6.44\, \text{m/s}\) to find \(v_{x0}\): \[v_{x0} = 6.44 \times \sin(52.0^{\circ}) = 5.08\, \text{m/s}\] (approximately)
04

Compute Horizontal Distance

To find the horizontal distance traveled by the shell, use the formula: \[x = v_{x0} \times t\] Where \(t = 6.00\, \text{s}\): \[x = 5.08 \times 6.00 = 30.48\, \text{m}\] (approximately)
05

Final Velocity Components Calculation

Calculate horizontal velocity component just before the impact: \(v_x = v_{x0} = 5.08 \, \text{m/s}\) Calculate vertical velocity component using: \[v_y = v_{y0} + gt\] Substitute: \(v_{y0} = -5.0\, \text{m/s}\), \(g = 9.81\, \text{m/s}^2\), and \(t = 6.00\, \text{s}\): \[v_y = -5.0 + 9.81 \times 6.00 = 53.86\, \text{m/s}\] (downward)

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Vertical Motion Analysis
When analyzing vertical motion in projectile problems, it is important to understand how objects move under the influence of gravity. The vertical motion is typically described using the equations of motion for uniformly accelerated motion. These equations account for the initial vertical velocity, acceleration due to gravity, and the time of flight.

In this problem, a shell is dropped from a height of 720 meters and takes 6 seconds to reach the ground. The equation used: \[y = v_{y0}t + \frac{1}{2}gt^2\]helps us find the initial vertical velocity component \(v_{y0}\). Here, \(g = 9.81 \, \text{m/s}^2\) is the acceleration due to gravity acting downwards. By setting the vertical displacement \(y\) as -720 meters (indicating a downward movement), combined with the known time, we can solve for \(v_{y0}\). This approach gives insight into how a body behaves under gravity alone, disregarding any other forces.
Velocity Components
Understanding velocity components is essential when analyzing projectile motion, which breaks down the velocity into horizontal and vertical components. Given an initial velocity at an angle, tools from trigonometry are typically employed to find these components.

In this exercise, the plane's velocity is given at an angle of 52 degrees to the vertical. To find the full velocity of the shell, we decompose the velocity into vertical and horizontal parts using: - For the vertical component, use \(v_{y0} = v_0 \cos(\theta)\)- For the horizontal component, use \(v_{x0} = v_0 \sin(\theta)\)

Using these relationships helps understand each motion direction's contribution. For example, the vertical component determines how the shell falls, while the horizontal component describes its travel along the ground.
Trigonometric Relations
Trigonometric functions are vital in physics, especially when dealing with angled movements. By utilizing sine and cosine, one can decompose a vector into its orthogonal components. This is particularly useful in projectile motion to separate a single velocity vector into horizontal and vertical velocities.

In the given problem, the angle of 52 degrees is with respect to the vertical. The cosine function relates to the adjacent side (vertical component) while the sine function relates to the opposite side (horizontal component). Specifically, the following equations are used:- \(v_{y0} = v_0 \cos(52^{\circ})\)- \(v_{x0} = v_0 \sin(52^{\circ})\)

These equations allow us to solve for the initial component velocities once the overall initial speed \(v_0\) is determined. Understanding these trigonometric relations provides a conceptual foundation for resolving vectors into their components.
Equations of Motion
Equations of motion provide a comprehensive toolbox for solving dynamics problems, particularly when dealing with uniformly accelerated motion such as an object in free fall. These equations offer a structured way to relate displacement, velocity, acceleration, and time.

The utility of these equations, like \(y = v_{y0}t + \frac{1}{2}gt^2\) for vertical motion, is evident in determining the height or flight time of a projectile. Similarly, the equation \(x = v_{x0} \times t\) allows us to calculate how far a projectile travels horizontally, given the constant horizontal velocity.

In this scenario, these fundamental equations assist in finding how a shell dropped from an aircraft changes velocity as it travels. They are based on simplifying assumptions, primarily that the shell's motion is only influenced by gravity once released. By understanding and applying these formulas, one can effectively analyze projectile motion.

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Most popular questions from this chapter

A moderate wind accelerates a pebble over a horizontal \(x y\) plane with a constant acceleration \(\vec{a}=\left(5.00 \mathrm{~m} / \mathrm{s}^{2}\right) \hat{\mathrm{i}}+\left(7.00 \mathrm{~m} / \mathrm{s}^{2}\right) \hat{\mathrm{j}}\). At time \(t=0\), the velocity is \((4.00 \mathrm{~m} / \mathrm{s}) \hat{i}\). What are the (a) magnitude and (b) angle of its velocity when it has been displaced by \(10.0\) \(\mathrm{m}\) parallel to the \(x\) axis?

The velocity \(\vec{v}\) of a particle moving in the \(x y\) plane is given by \(\vec{v}=\left(6.0 t-4.0 t^{2}\right) \hat{\mathrm{i}}+8.0 \hat{\mathrm{j}}\), with \(\vec{v}\) in meters per second and \(t\) \((>0)\) in seconds. (a) What is the acceleration when \(t=2.5 \mathrm{~s} ?\) (b) When (if ever) is the acceleration zero? (c) When (if ever) is the velocity zero? (d) When (if ever) does the speed equal \(10 \mathrm{~m} / \mathrm{s}\) ?

The acceleration of a particle moving only on a horizontal \(x y\) plane is given by \(\vec{a}=3 t \hat{\mathrm{i}}+4 t \hat{\mathrm{j}}\), where \(\vec{a}\) is in meters per secondsquared and \(t\) is in seconds. At \(t=0\), the position vector \(\vec{r}=(20.0 \mathrm{~m}) \hat{\mathrm{i}}+(40.0 \mathrm{~m}) \hat{\mathrm{j}}\) locates the particle, which then has the velocity vector \(\vec{v}=(5.00 \mathrm{~m} / \mathrm{s}) \hat{\mathrm{i}}+(2.00 \mathrm{~m} / \mathrm{s}) \hat{\mathrm{j}}\). At \(t=4.00 \mathrm{~s}\), what are (a) its position vector in unit-vector notation and (b) the angle between its direction of travel and the positive direction of the \(x\) axis?

A plane flies \(483 \mathrm{~km}\) east from city \(A\) to city \(B\) in \(48.0 \mathrm{~min}\) and then \(966 \mathrm{~km}\) south from city \(B\) to city \(C\) in \(1.50 \mathrm{~h}\). For the total trip. what are the (a) magnitude and (b) direction of the plane's displacement, the (c) magnitude and (d) direction of its average velocity, and (e) its average speed?

A purse at radius \(2.00 \mathrm{~m}\) and a wallet at radius \(3.00 \mathrm{~m}\) travel in uniform circular motion on the floor of a merry-go-round as the ride turns. They are on the same radial line. At one instant, the acceleration of the purse is \(\left(2.00 \mathrm{~m} / \mathrm{s}^{2}\right) \hat{\mathrm{i}}+\left(4.00 \mathrm{~m} / \mathrm{s}^{2}\right) \hat{\mathrm{j}}\). At that instant and in unit-vector notation, what is the acceleration of the wallet?

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